An extrusion press is used for extruding aluminum frame parts or other metal products. In past extrusion presses, the starting material, that is, the billet, was loaded into a fixed container. This was then pushed by an extrusion stem driven by a ram cylinder (hydraulic cylinder). The billet was made to pass through a die positioned to the outlet of the container to thereby be extruded to a predetermined cross-sectional shape. Specifically, the billet loaded in such a molding machine is supplied by a billet loader. The billet loader grips a billet sent from a billet carrier arranged at the side of the molding machine and conveys it to the billet loading opening of the container. It loads the transferred billet into the container pushed by the extrusion stem in the state with the billet and loading opening centered. After that, the billet is extruded under pressure whereby it is formed into the shape of the final product.
Among the products extruded by an extrusion press, there are aluminum frame members and other long products. In the case of long products, the extrusion stem pushes the billet for a long period of time. For this reason, a hydraulic cylinder able to operate with a long stroke at a high pressure has been used for the ram cylinder for pushing the extrusion stem. However, such a conventional extrusion press device has been driven by hydraulic pressure, so there were challenges such as protection of the environment (against noise, oil leakage, etc.), reducing energy consumption (lowering running costs), etc. To meet these challenges, realization of a press using the electric powered drive system employed in plastic injection molding machines or die cast machines for die casting aluminum alloys has been demanded. In the case of an electric powered drive system, in general, it is necessary to convert the rotary motion of a first stage drive device comprised of an electric motor to linear motion or back and forth linear motion.
In conventional hydraulic cylinder devices, the larger output capacity sought from an extrusion press, for example, 9800 kN (that is, 1000 tf) or more, can be continuously output. However, no mechanism has yet been realized for converting rotary motion to linear motion taking the place of conventional hydraulic cylinder devices. Therefore, electric powered drive systems have not been applied to extrusion presses.
A conventional extrusion press is a machine using a motor and pump to drive a plurality of hydraulic devices to produce an extruded product. During the extrusion process of course and also processes other than the extrusion process, for example, even in the discard cutoff step, billet loading step, etc. as well, the same pump and motor are used as sources of drive power. Here, the extrusion-use pump and motor utilizing hydraulic devices and an auxiliary pump and motor have to be kept constantly operating in an idling mode even when not directly required for operation of the extrusion press device. Power loss therefore occurs.
Further, when a machine user uses a machine for a long time, maintenance and inspection are required for continued operation. Comparing when the drive source is a hydraulic source and when it is only an electric motor, it is believed that the time required for maintenance would be overwhelmingly longer in the case of a hydraulic source. The reason is that when using hydraulic equipment for many years, the hydraulic fluid degrades, the valves become worn, fluid leaks from the pipe joints, and other trouble occurs at the pumps, valves, manifolds, piping, and numerous other parts. Much time is required for identifying the causes of the trouble and taking measures against them. In this way, there were the following defects in conventional hydraulic drive type extrusion presses:
(1) Since hydraulic fluid was used as the medium for the drive force, realization of the speed and precision of position crucial to mechanical operation was difficult.
(2) The energy loss was relatively great and cooling water was required for preventing a rise in fluid temperature, so the running costs swelled.
(3) A hydraulic circuit has many high pressure components and generates high noise at the time of operation.
(4) Since a large amount of hydraulic fluid is used, leakage of the hydraulic fluid causes problems in maintenance, the environment, and costs while disposal of the hydraulic fluid causes problems in the environment and costs.
To deal with these problems, PLT 1 proposes a completely electric powered type extrusion press. In this prior art, the extrusion drive device is provided with four electric powered extrusion-use main motors for driving a single extrusion stem. Four wire drums are driven to rotate by the respective electric powered extrusion-use main motors so as to make the crosshead to which the extrusion stem is fastened move back and forth. Each wire drum has first ends of 10 single strand wires fastened to it. The other ends are fastened to a crosshead fastening member. Each wire is strung straight without anything interposed between the wire drum and the crosshead connecting member. The four wire drums are made to simultaneously rotate to wind up the wires in a simple manner and make the crosshead move back and forth. In this prior art, rotary motion is converted to linear motion by the plurality of wires being wound up on the wire drums, but the wires are just linearly connected, so the output is insufficient. For this reason, four electric powered extrusion-use main motors had to be used. Further, 10 wires had to be attached between each wire drum and crosshead connecting member by a uniform tension (unless uniform tension, the load will be applied to a specific wire and cause breakage or other issues). Installation and adjustment were extremely troublesome.